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EML2322L Midterm
Notes for EML
| Question | Answer |
|---|---|
| The first step to the design process is research T/F | True |
| What does a tap handle do? | holds taps so torque can be applied |
| What is a tap? | Used to create internal threads in a workpiece |
| What is a tap guide (spring loaded)? | Holds tap handle perpendicular to the workpiece |
| What is an endmill? | A rotating cutting tool that can cut with its end(axially) or with its sides (radially). Creates shoulder, edge, or face in a workpiece. |
| What is a center drill? | short, stiff cutting tool used to accurately start a hole |
| What is a drill? | Rotating cutting tool that cuts only with its end (axially), used to create holes |
| What is an edge finder? | Used to locate edges (i.e. datums) or parts or features |
| What is a center finder? | Used to locate centers or cylindrical parts or features |
| What is a reamer? | Used to create extremely accurate holes in workpieces; used only as a final operation after drilling the hole 1/64" under the final size |
| What is a countersink? | Used to create conical holes in which countersink (flathead) screws can sit flush or slightly below the surface of the part |
| How are requirements determined? | Based on what the assembly needs to do, the constraints (money, parts, size), how the features will generate the function. |
| Male fasteners | Hex head, slotted head, flat (or countersunk) head, round head, socket (or "allen") head, button head and socket set screw. |
| Female fasteners | Nuts: hexagonal nuts and nylon ring elastic stop nuts ("lock nuts") |
| What is the functional difference between a bolt and a screw? | A bolt always requires a nut and a screw does not. |
| What does lead mean in fasteners? | The linear distance that a point on a fastener thread will advance axially in one revolution (equal to the pitch of the fastener). i.e. how far it travels linearly. |
| Thread root | Peak of the thread. |
| Head | The enlarged shape to provide a bearing surface and a method of turning (or holding) the fastener. |
| Bearing surface | the supporting surface of a fastener with respect to the part it fastens. |
| Grip length | The length of the shank |
| Thread length | Length of threaded portion of the fastener which is a function of the fastener diameter. |
| Two types of thread | Fine and Coarse threads. |
| Basic rule for fastener selection | Fine threads are stronger when the female thread is strong relative |
| How should engineers prevent relative sliding of parts fastened to each other? | Use pins, dowel, and locating shoulders |
| Fastener threads should never be placed in ________. Why? | Shear. Transverse shear will loosen the screw. The threaded portion of a bolt has less surface area than the shank which means less bearing area to the joint. Material will be removed from internal thread. |
| What keeps a fastener tight or secure? | Adequate torque |
| Pitch | Distance between thread crests and is equal to 1/thread length. |
| Overtightening is better than under tightening T/F | True |
| How to find torque of a screw? | (1) Find the yield torque from chart (2) Multiply by 0.9 to get tensile stress (3) Find the Preloaded force F by multiplying tensile stress with given area (4) T = 0.2 * F * d where d is the major diameter |
| How are fasteners called? | Standard use the shank size - TPI. If smaller than 1/4" are referred to by "screw size" designations. Metric ex. M6x1.0 where 1.0 mm is pitch |
| Tapdrill | The final drill size prior to using a tap to cut threads into the hole. If the hole is too small, the tap will break when trying to create the threads; if it is too large, the threads will be weak and fail in shear. |
| Clearance drills | Used for clearance holes for fasteners, shafts, or pins. You can find the clearance number by subtracting the diameter by the clearance shown on a tap and drill chart. |
| Close fit clearance holes | Used when you want a more accurate bolt pattern (i.e. when using the DRO on the milling machine). |
| Free fit clearance holes | Used when you want to save time and make the clearance holes more quickly (i.e. when using a drill press). |
| Fastener join stability rule | Never place fastener holes closer than one major diameter to a workpiece edge. |
| Radial clearance | Half of the clearance |
| Blind holes | Add one major diameter to the required depth. Holes that go to a certain depth, this allows for full engagement of threads. |
| How do the fastener grade and TPI affect the required preload? | As the fastener grade and TPI increase, so does the desired preload |
| Lathe turning | A metal cutting process used for the generation of cylindrical surfaces. Workpiece is rotated on a spindle and the tool is fed into it radially, axially, or both ways simultaneously. Generation of any cylindrical surface with a single point tool. |
| Held in a chuck | Clamped in a rotary chuck containing 3 or 4 jaws. |
| Held in a collet | It is held in precision cylindrical bushings |
| Held between centers | Supported by 2 pointed mandrels. Used for long, slender workpieces. |
| All standard tool holders are designed to cut with the cutting edge or point located on the centerline of the machine and workpiece. T/F | True |
| Nominal Size | The size used for general description (i.e. 3/4" shaft). Standard measurements. |
| Basic Size | The size is converted to pure decimal form which deviations are made to produce limit dimensions |
| Limit tolerance | Upper and Lower limit |
| Unilateral tolerance | +/- a separate number |
| Bilateral tolerance | +/- same number |
| Fit | The general term to describe the range of tightness designed into parts which assemble one into another. |
| Allowance | An alternative term for tightest possible fit |
| Clearance fit | A fit in which one part fits easily into another with a resulting clearance gap. Aim lower. |
| Interference fit | A fit in which one part must be forcible fitted into another. Aim higher. |
| On the lathe, the x-axis on the DRO is reading what workpiece measurement | Diameter |
| When taking a roughing pass on an aluminum workpiece, cutting oil is necessary T/F | True |
| When filing on the lathe, the chuck can still be run at the same RPM that was used for machining. T/F | False |
| On the milling machine, the speed should never be adjusted when the machine is off. T/F | True |
| What speed are edge finders used? | 1000 rpm |
| All drilling operations require oil. T/F | True |
| You center drill more than 1/2 the tip of the drill bit. T/F | False. You cannot drill more than 1/2 of the tip. |
| What is the step up size? | 1/4" or 0.250" |
| Difference between twist drill and endmill? | Endmill can use its sides and bottom to cut and it has a flat bottom. Twist drill has a conical bottom and only uses bottom to cut. |
| What does MIG mean? | Metal Inert Gas |
| Why are decision matrix objectives weighted? | Not all decisions are of equal importance. |
| Concern with having too many objectives? | Each objective has a small weighing factor to contribute. |
| First design step | Research and plan |
| What does a 35 degree lathe cutting tool do? | Turns the side of a cylindrical piece. |
| What does a 80 degree lath cutting tool do? | It turns the side and profiles the face of a cylindrical piece. |
| What is the call out for 4, 1/4" screw holes, into aluminum with a depth of 0.5". | 0.201" depth of 0.75" 1/4-20 UNC depth of 0.5" 4 PLACES |
| How many full threads of engagement will a 1/4" fastener with a depth of 0.5" have? | TPI x Depth. (0.5 in) x ( 20 threads/in) = 10 threads of engagement |
| 1/4" screw has a tensile strength of 130,000 psi and area of 0.031 in^2. How much force needs to be applied to reach 80% yield? How much torque is needed? | σ= F/A ➝ F = (0.8)σA= (0.8)(130,000 psi)(0.031) = 3224 lb. T = F * D = (3224 lb)(0.25 in) = 806 lb * in. |
| What is the purpose of a fastener? | To clamp parts together. |
| Tap drill for 1/4" fastener to thread steal? | 0.228" UNF |
| M10 Fastener, Cast Iron | 9.20 mm depth THRU M10 x 1.25 depth THRU # PLACES |
| Provide the sequence of cutting tools + tool sizes to make a hole pattern of 8 M10 fasteners in cast iron. | 1) Center Drill 2) 1/4" twist drill 3) 23-64" (9.20 mm) drill 4)M10x1.25 tap, tap handle, tap guide |
| Bolt holes are always clearance holes T/F | True |
| Workpiece in lathe rotates about z-axis. T/F | True |
| Workpiece in the mill rotates about x-axis. T/F | False the workpiece does not rotate. |
| Most common work holding device for a milling machine? | Vise |
| Generation of surface perpendicular to rotational axis of a workpiece/tool is referred to as? | Facing |
| All standard lathe tools are design to cut with the cutting edge located on the centerline of the workpiece. T/F | True |
| Purpose of a tolerance table | Establishes standard, reduces clutter. |
| What is tolerance stack up? | This occurs when doing tolerance loops using vectors to make sure that the parts will still fit together as long as they're within tolerance. |
| Lathe extra stock lengths for installing part. | Working length 0.6 in and clearance 0.25 |
| How to check relief angles? | Relief angles are adjusted by loosening the nut on the top of the tool post and rotating the tool post. You want an angle of 5 degrees. |
| Do you have to zero the z-axis after doing a pass in the lathe? T/F | True |
| How to zero in the lathe? | z-axis: Destructive zero on the face by making a shiny ring and sound of contact. x-axis: Destructive zero on the OD |
| What is the centerline gauge? | This checks if the tool is aligned. Move in x and z axis. |
| When cutting on the bandsaw how much length do you need to add? | You need to add 1/8" to accommodate for the tolerance. |
| What is electric arc welding? | An electric power supply creates an arch which melts the base metal to form a molten pool. A filler wire is added and the molten pool is allowed to cool. |
| How can oxidation be avoided when welding? | A flux or gas is used to create an inert environment in which the molten pool can solidify without oxidizing. |
| Methods for attaching parts with a spot welder? | Overlapping the edges of parts. L-brackets. |
| What is the maximum thickness of sheet metal before it is considered a plate? | 0.25" |
| What size hole should be made in 20 GA steel sheet metal for a 10-24 screw. | 0.201" 0.196" |
| PPE for welding | Safety glasses, welding gloves, welding jacket, welding helmet. |
| Welding without protective clothing can result in sunburn. T/F | True |
| What are important steps to take before welding to ensure safety of others inside and outside the welding bay? | Call "Eyes", Wait two seconds after calling "eyes" before beginning to weld. Be sure the curtain is closed. |
| What are the drawbacks of stick welding? | It is a slow process. There is a lot of post-weld clean up required. It produces a lot of smoke. NOT: Expensive |
| Which type of welding results in the strongest welds? | TIG |
| Which type of welding is the fastest? | MIG |
| Which types of welding result in contaminant-free welds? | MIG, GTAW, TIG. Not: Stick |
| When bending sheet metal, the bend angle is typically _____ than expected. | Smaller |
| In ______ the slug is the part, and the remaining sheet metal is discarded. | Blanking |
| The maximum punch force is directly proportional to the ultimate tensile strength of the sheet metal. T/F | True |
| When bending sheet metal, the inner fibers are in _____ and the outer fibers are in _______. | Compression, Tension |
| What is commonly used in industry for bending sheet metal? | Press Brake |
| What is spring back a function of? | Thickness, angle of attempted bend, type of material being bent. Not: Length of material bent |
| What is SMAW/Stick welding? | Shielded metal arc welding uses a voltage source and a flux covered metal electrode "sticks" to carry the electrical current. Good: Cheap, portable, versatile (can weld various metals & thicknesses). Bad: Slow, dirty, requires clean up and more skill. |
| What is GMAW/MIG welding? | Gas metal arc or metal inert gas welding uses a wire electrode that gets consumed as the metal melts. Oxygen-free gas is used to shield and produce an inert environment. Fast, versatile, clear. Bad: requires shielding gas, minor post-weld clean up. |
| What is the GTAW/TIG welding? | Gas tungsten arc or tungsten inert gas uses a tungsten electrode and filler metal (same as base metal). It requires shielding (noble) gas. Good: Highest quality, versatile, no cleanup. Bad: slow, requires gas and skill. |
| What is chamfering? | A tool cuts the corner of a cylinder at an angle. |
| What is boring? | A single point tool is fed linearly and parallel to the axis of a workpiece to enlarge a hole made by a previous process in the operation know as boring. |
| What is milling? | A process of generating machined surfaced by progressively removing a predetermined amount of material or stock from the workpiece which is advanced at a relatively slow rate of movement or feed to a milling cutter rotating at a high speed. |
| From what material are most solid milling cutters and drills made? | HSS |
| What is sand casting? Not on exam | You make pattern, sand mold, and then the part. Least expensive. Moist sand is tightly compacted around patterns, which are then separated and cured into a solid mold. You pour the metal inside when you bring them back together and they are single use. |
| What is investing casting? Not on exam | Wax pattern using a die, coat in ceramic, melt the wax which leaves the ceramic mold. You pour the metal into the mold and then remove the final part via vibratory methods. More expensive and single use. |
| What is die casting? Not on exam | Machine mold then part. Can be most expensive. |
| What is extrusion (Billet)? | You melt material and then have it cool down to roll into different shapes. This is what stock material is. |
| What is forging? | You hit hot stuff with a hammer. The repeated deformation of heated solid metal refines the grain structure and improves the part strength without adversely affecting the material's ductility. |
| List in order of strongest to weakest. Casting Forging and Extrusion. | Forging, Extrusion, and Casting. |
| What is casting? | Pouring molten liquid into a mold where it will cool down and solidify. The metal shrinks when it is cooled which makes mold design a complex undertaking and final surface finish and feature tolerances are low. The grain pattern is random so weaker. |
| What does CNC mean? | Computer numeric controlled. Computer electronically controls the movements. Can have up to 4 axes. XYZ and rotation axis. This allows for contouring ability. |
| Benefits of a CNC machine? | Allows for complex contours and internal features. Increases productivity and quality control by allowing multiple parts to be produced using the same program and tooling. |
| What parts have advantages when CNC is used? | (1) Simple parts that are mass produced and/or (2) complex parts with features requiring multiple axes of simultaneous motion. |
| Misconception of CNC machine? | Does not inherently increase part accuracy. An old CNC with a lot of hours of use will produce less accurate features than a new quality manual machine and vise-versa. Accuracy has more to do with machine design, component selection, and mechanical wear. |
| Downsides of a CNC machine. | Higher initial cost, larger space and electrical requirements, increased maintenance costs, required programming skillset and their inherent complexity means there's a higher probability of component failure during the use of lifespan. |
| When do you use coarse threads and why? | When the material is weak because you want to give the female threads (the material) the advantage. Coarse threads have a smaller minor diameter increases the shear area resulting in higher static strength and fatigue resistance in female threads. |
| When do you use fine threads and why? | You use them when the material is strong because you want the male threads to have the advantage. The cross-sectional area increases resulting in higher static strength and fatigue resistance in male threads. |
| Why aren't all threads engaged? | The fastener has elasticity like a spring and to achieve 90% yield strength you only need 5 threads to be engaged. Check this. |
Created by:
ncam0720
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